This work proposes the design of the sensors for an independent multiphase flow rate meter which shall be composed of two parts: (a) a differential pressure meter and (b) an electrical impedance tomograph test section, consisting of 32 electrodes. The first sub-system shall measure pressure difference and its fluctuations around a restriction in the duct. The second sub-system is the interface with the flow for an electrical impedance tomography device. This meter will be tested with an air-water 2 inch diameter facility at the Multiphase Laboratory at the University of São Paulo. The data obtained from the set of sensors shall be sufficient for the determination of the flow pattern and the estimation of the flow composition and the multiphase flow rate, in a future contribution.

In risers, the most common flow pattern is intermittent or slug, characterized by an intermittent axial distribution of gas and liquid. This flow pattern may change dramatically under certain geometric and flow conditions leading to an undesirable hydrodynamic instability known as severe slugging. It may have a period of hours, causing higher average pressures, instantaneous flow rates and oscillations at the reservoir. These conditions may lead to the oil production shutdown. Many studies were performed in air-water systems and many stability criteria were developed based on simplified models for vertical risers. Although the stability criteria are useful for a first estimation of the unstable region, a common drawback is that they were not derived from complete dynamic system models, but from ad-hoc conditions in which many physical effects were disregarded; consequently, their applicability is quite limited. As a more efficient alternative to time domain simulations, the linear stability analysis is a powerful technique to identify the stable and unstable regions. In this paper, a stability solver for hilly terrain flow is presented. This solver is an extension of the methodology adopted in the authors’ previous works considering a general approach for the void fraction and friction drop through the determination of the local pattern flow.

The present work is concerned with the prediction of annular pressure buildup (APB) in an offshore well. APB is caused by the heating and expansion of the annular fluid trapped between the production line and the surrounding formation due to the production of heated hydrocarbons. To better predict this effect a mathematical model was developed to simulate the hydrodynamic and thermal processes along the production well, as well as the thermal and mechanical interaction with the surrounding formation. The model was developed to be as robust as possible so it can be used in different scenarios. The thermal model relied on the energy equation for the hydrocarbon mixture and on a thermal resistance network in the radial direction. The momentum and energy equations were solved coupled to determine the vapor mass fraction and the equilibrium temperature of the mixture along the well. An estimate of the annular pressure buildup was obtained by coupling the expansion of the trapped fluid with a structural deformation model of the concentric annuli. The results, which are compared against pressure and temperature field data for a 4700-m deep offshore well composed by three concentric annuli with a permanent downhole gauge (PDG) 3890-m deep, focus on the temperature, heat transfer rates per unit length and APB.

We present an experimental work on the development and implementation of a technique to process digital images obtained by high-speed recording of the onset of intermittent flows (slug and plug) in a 26.4-mm ID circular pipe. The processing algorithm was based on the Canny edge detection method to determine the position of the interface. Indirect back illumination of the flow was provided by two 130-W (60 kLux) LED sources to enhance the contrast between the phases in the images. The image acquisition frequency was set at 200 Hz. Quantitative results on the formation of ‘slug precursors’ and their growth into liquid slugs are presented as sequences of still images of the inlet region. Frequency data obtained from the evaluation of the power spectral density of the image sequences were in good agreement with a similar analysis carried out for capacitance sensor data.

Polo – Research Laboratories for Emerging Technologies in Cooling and Thermophysics, Department of Mechanical Engineering, Federal University of Santa Catarina, Florianopolis, SC, Brazil

Condensation of vapors in vertical and inclined channels is encountered in a number of applications. In this paper, we present a mathematical model based on momentum and energy balances in annular flow (considering the superheated vapor and non-equilibrium vapor-liquid regions) to predict the heat transfer parameters associated with the condensation of R-134a in a 5-mm ID 950-mm long inclinable tube. The model results are compared with the experimental data of Barbosa et al. (2016), showing a good agreement.

Grain flows through pipes are frequently found in industry, such as in pharmaceutical, chemical, petroleum, mining and food industries. In the case of size-constrained gravitational flows, density waves consisting of alternating high- and low-compactness regions may appear. This study investigates analytically the dynamics of density waves that appear in gravitational flows of fine grains through vertical and slightly inclined pipes. The length scales of density waves are determined using a one-dimensional model and a linear stability analysis. The analysis exhibits the presence of a long-wavelength instability, with the most unstable mode and a cut-off wavenumber whose values are in agreement with previously published results.

Multiphase flows in pipeline-riser systems in oil production offshore system may not have a steady state under certain flow and geometric conditions. In this case, the flow is intermittent, usually periodic, and may lead to harmful operation conditions and, therefore, the oil production shutdown. Linear stability analysis of an adequate flow model reveals the regions in the parameter space where a steady flow operation regime exists. This work presents and discusses different strategies to perform the numerical linear stability analysis of an adequate model for two-phase flows in pipeline-riser systems with and without friction along the riser. The two-phase model consists of a system of partial-differential algebraic equations (PDAE). Therefore, topics from the theory of differential-algebraic equations (DAEs) are used in the different strategies to perform numerical linear stability analysis. Our results show that different strategies lead to very similar stability maps, as expected.

The effect of hot spots on the heat removal efficiency during flow boiling in micro-scale channels is still an open issue in the literature. Despite of its importance, this subject has attracted the attention of only few authors, especially regarding flow boiling in single-channels. In this context, the present study concerns an experimental investigation on the effects of local high heat fluxes on convective boiling in a micro-scale channel of 1.1 mm ID for HFC-134a, saturation temperature of 33°C and mass velocity of 1600 kg/m²s. The hot spot is a segment of the test section 10 mm long in between two segments 40 mm long. Experimental results were obtained, firstly, for a constant heat flux of 80 kW/m² at the hot spot and a background heat flux of 40 kW/m² for the regions of the test section upstream and downstream of the hot spot. Then, experiments were performed for pulsating heat fluxes at the hot spot, varying sinusoidally with amplitude ranging from 5 to 20 kW/m², frequencies of 0.5 Hz and 1 Hz and a fixed RMS value of 80 kW/m². The transient behavior of the heat transfer coefficient was evaluated at the hot spot and also at its upstream and downstream regions. It was found that the amplitude of the oscillation of the heat transfer coefficient at the hot spot increases with an increment in amplitude of the heat flux oscillation. Moreover, the heat transfer coefficient and the heat flux oscillate at the same frequency. During transient tests, it was observed that the heat transfer coefficient at the region upstream the hot spot increases with varying the heat flux at the hot spot. However, this augmentation was within the range of uncertainty of the heat transfer coefficient measurements.

In order to study the two-phase flow dynamics inside an industrial Venturi scrubber, the present work compares numerical simulations employing the standard k-ε turbulence model and the Eulerian-Lagrangian method with different droplet breakup models, as implemented in ANSYS CFX 15.0, with experimental data. It is also compared the influence of liquid injection in the droplet dispersion inside the Venturi scrubber, which was achieved by comparing injecting droplets with the same diameter and injecting droplets with a size-distribution (Rosin-Rammler). A better liquid dispersion was achieved using CAB model.

An experimental analysis of the pressure drop induced by an orifice plate on a mixture of air and water flowing horizontally in slug regime is carried on. The pressure drop is not steady, but fluctuates around a mean value due to the intermittent nature of the slug flow. The analysis focus on the pressure drop mean value and its fluctuation around the mean value, the correlation between high and low pressure fluctuation and the occurrence of gas at the orifice throttle. Also the signal time and frequency domain are explored l. The experimental work is developed employing a fixed liquid and gas superficial velocities of 0.3 m/s and 0.5 m/s, respectively, and explore the effects of the area contraction ratio and the orifice plate distance from the air-water mixer.

Pipe blockage due to gas hydrate formation is a main concern to the oil and gas industry due to the costs of production interruptions. Hydrate formation scenarios are usually found in offshore production pipelines, where oil and gas flow along the pipeline as a mixture that may also contain sand and brine. The high pressure conditions and the heat transfer with the external medium – the ocean – may create the necessary conditions for hydrate formation. Hydrates may form: (i) as a deposit on the pipe inner wall, where the temperature gradient is higher and the wall imperfections trigger the nucleation process; or (ii) in the gas-water interface, where a more effective contact between the phases occurs, forming a hydrate-in-liquid dispersion. This work gathers three years of study from NUEM – Multiphase Flow Research Center on slug flow modeling using a mechanistic approach and shows the main equations, results and discussions of: (i) slug flows with heat transfer; (ii) mass transfer and heat generation during hydrate formation; (iii) hydrate formation as a layer deposited on the pipe wall; and (iv) hydrate formation as a dispersion, thus creating a new flowing phase. A theoretical discussion about the possible mechanisms of transition between dispersion and wall deposition is also included in the article, focusing on: (i) whether the hydrate dispersion deposits and (ii) whether hydrate particles may detach from the wall to suspend in the liquid as a dispersion.

The heat transfer between the deep sea waters and the oil and gas mixtures flowing through production lines is a day-to-day situation in the petroleum industry. The optimum prediction of the liquid-gas flow parameters along those lines, where the slug flow pattern is predominant, has an extreme importance in the design of production facilities. The mixture temperature drop caused by the colder sea waters directly affects physical properties of the fluids such as the viscosity and specific mass. Gas expansion may also occur due to pressure and temperature gradients, thus changing the flow hydrodynamics. Several models have been developed to characterize this kind of flow along the pipeline. When dealing with long pipelines, it is important to choose a less expensive model, such as the mechanistic ones. These models are, however, not yet prepared for taking the gas contribution in momentum and energy balances into account – which cannot be neglected when dealing with the frequently high pressures found at the inlet of long pipelines. With this challenge in mind, the present work extends a mechanistic approach for characterizing the slug flow hydrodynamics and heat transfer to account for the effects brought by the gas to the conservation equations, with a special focus on the energy balance. Terms due to the gas expansivity, the gas heat capacity and the heat transfer between the gas and the wall are introduced in the model. Results are shown as to evidence the gas contribution in higher pressure scenarios, when the gas contribution is not negligible. The parameters analyzed are the mixture temperature, pressure and heat transfer coefficient and the gas superficial velocity.

Particle Imaging Velocimetry (PIV) measurement in gas-liquid bubbly flows is a challenging task, mainly due to the dispersion of the laser light caused by the gas-liquid interfaces. A common solution adopted is the use of fluorescent seeding particles associated with a bandpass filter for the laser light. Therefore, the camera captures only the light fluoresced by the seeding particles, filtering the laser light dispersed by the gas-liquid interfaces and measuring a velocity field which corresponds to the liquid phase, where particle seeding occurs. However, even for relatively low gas fractions, the fluoresced light reflected by the interfaces distorts the measurements, due to the fact that the reflected particles are out from the laser plane. In addition, the fluoresced light also reflects at the interfaces, distorting the measurements and trending to overshoot the measured liquid velocities. In this work, PIV measurements of air water bubbly flows are performed with fluorescent tracer particles (PIV/LIF). A method was developed to overcome the problems caused by the presence of bubbles in the flow, which uses the pixel intensity information of the interrogation window from each velocity vector. The proposed method was tested for three air-water flow configurations, from low to moderate void fractions (up to approximately 9.0 %). From the two-phase flow experiments, the method described in this work is capable to measure the liquid velocity and it is shown that without the correct treatment, the void fraction can be overestimated.

An analysis of the initial behavior of free surface liquid flows on inclined planes is presented. The surface of the liquid, under some conditions, may present long-wave instabilities. These instabilities may evolve to surface-waves, that often appear on thin liquid films. Such knowledge is useful in industry, once liquid films help to remove the heat from solid surfaces, and also reduces the friction between high viscosity fluids and pipe walls, by injecting, close to the wall, a less viscous fluid. The surface-waves instability phenomena are governed by the Orr-Sommerfeld equation and their boundary conditions. In this work we present a long-wave solution through an analytical and numerical approaches for the Orr-Sommerfeld equation based on asymptotic and Galerkin methods. Both methods are compared with previous works for validation. The solution gives the critical conditions in which the liquid film turns unstable, and describes possible features that produce these instabilities. All codes, data and plots were produced in the MATLAB environment.

In this work the process of filling fractures through the injection of solid particles into a flow is investigated experimentally. The experimental set-up comprises a rectangular test section with a transverse fracture, instrumented with pressure gauges, flow and temperature monitors. In order to characterize the fracture filling pattern, the influence of variations of the fracture thickness (16, 20 and 26 mm), the fracture outlet initial flow rate (from 0.25 to 1.25) and the Reynolds number (150, 300 and 450) along the position, length and height of the formed bed of particles is investigated. The particulate flow is represented by a solution of water-glycerin with abrasive plastic – Urea particles. Results show that all the parameters present the ability to modify the geometric characteristics of the bed, having a direct influence on the filling time and the fluid lost by the fracture.

Francis Turbines operating at overload condition may have their overall dynamic behavior affected either by forced or self-excited pressure pulsations in the hydraulic system. Self-excited pressure pulsations may be triggered by the existence of a typical cylindrical axisymmetric cavitating vortex rope inside the conical region of the draft tube induced by the swirling flow leaving the Francis runner. This vortex might act as a destabilizing element in the hydraulic circuit depending on it compliance and mass flow gain factors. This work presents an overload surge investigation based on prototype measurement results for a medium head Francis Turbine Power Plant. Firstly, the prototype measurement results are presented. A stability analysis based on the eigenvalues of a linearized 1D model of the hydraulic circuit as a function of the vortex rope parameters is then performed. Steady State biphasic CFD simulations are used to estimate the vortex rope properties for the same prototype operating points. Upcoming CFD simulations based on a 1D/3D coupled system should improve the numerical prediction of the phenomenon.

This work presents a new transient hybrid model to simulate the gas-liquid slug flow pattern in pipes. A slug tracking methodology was integrated to a two-fluid slug capturing model and, as a result, the new model will be able to simulate the initiation of the slug flow from the stratified pattern and track the unit cells (structures composed by a slug and an elongated bubble) with a low computational effort. A simulation was carried out for a 40 [m] pipe, with a change of direction from horizontal to a 5o upward inclined pipe. The results and computational cost of this new hybrid code were compared to those from the slug capturing. A reduction of more than 50% in the computational effort along with similar results for bubble length, slug length, slug frequency and pressure gradient was achieved.

The present paper addresses an experimental investigation of flow-induced vibration (FIV) during two-phase air-water flow across a normal triangular tube bundle, counting with tubes of 19 mm O.D. and transverse pitch per diameter ratio of 1.26. The experimental approach features a tube mounted in cantilever, which is instrumented with two accelerometers perpendicularly mounted in the free tip. Based on measured acceleration power spectral densities, a study on dynamic parameters, such as hydrodynamic mass and damping ratio, is performed. Moreover, its variation with homogeneous void fractions ranging from 30% to 95% is analyzed and compared with results found in open literature. Furthermore, the current models used to predict the tube vibration upper-bound during FIV induced by turbulence induced mechanism are reviewed and implemented for the conditions of the experimental database from the present experimental campaign and gathered in the open literature. The dynamic parameters estimated with predictive methods showed good agreement with the experimental database, as well as the design guidelines for FIV induced by turbulence showed to be a reasonable design tool.

Gas hydrate is a main flow assurance concern for worldwide oil companies due to the high risk of pipe blockages. Those blockages represent a global obstacle to the successful production of deep-water hydrocarbons. Hydrates are crystals formed by the trapping of gas molecules into cages formed by hydrogen-bonded water molecules and may form at the water-gas interface. Right after the hydrate formation onset, when the volumetric fraction and the size of the particles are still small, the particles flow homogeneously dispersed in the liquid phase. However, the particles may interact with the gas-liquid flow, changing the flow hydrodynamics. For offshore operations, the phases are assumed as flowing predominantly in the slug flow pattern due to the range of gas and liquid superficial velocities in those operations. Understanding the effects of the solid particles introduction in the slug flow is essential to improve the efficiency and safety of oil and gas facilities. The purpose of the present work is to experimentally characterize solid-liquid-gas slug flow with the presence of homogeneously dispersed hydrate-like particles. Experimental tests were carried out with polyethylene particles of 0.5 mm-diameter with density similar to the hydrates (938 kg/m3). The test section comprised a 26 mm-ID, 9 m-long horizontal duct made of transparent Plexiglass. High Speed Imaging was used to analyze the bubbles shape behavior due to the introduction of the solid particles. Resistivity sensors were placed in the test section to measure the unit cell translational velocity, the slug flow frequency and the bubble and slug region lengths. Two distinct solid particles concentrations were tested (6 and 8 g/dm3) and compared to a similar case of liquid-gas slug flow.

The local heat transfer coefficient and flow patterns were studied experimentally during flow boiling of R-290 (propane) inside multiport extruded (MPE) mini channel tube made up of 7 channels with hydraulic diameter of 1.47mm. The tests analyzed the effects of heat flux, mass velocity and vapor quality. The study was performed with heat fluxes from 5.3 to 20 kW/m2, mass velocities varying from 35 to 170 kg/m2 and vapor quality between 0.07 to 0.98. As a result, heat transfer coefficients between 1-18 kW/m2K were obtained. Five types of flow patterns were observed, with predominance of plug, slug and churn. The results unveil the significant effect of flow patterns on the heat transfer characteristics.

This work aims to analyze the heat transfer performance during pool boiling of DI water on copper surfaces coated with maghemite nanoparticles. The nanocoated surfaces were produced by maghemite nanoparticle deposition, for different mass concentrations (0.029 and 0.29 g/l, corresponding to low and high nanofluid concentration, respectively), via boiling process of Fe2O3-deionized water nanofluid. Two sets of experiments were performed in this study to reveal the potential effect of nanoparticles deposition on the heat transfer. (i) Firstly, pool boiling of Fe2O3-DI water nanofluid were carried out on copper surface by applying heat flux in steps ranged from 100 to 800 kW/m²; and secondly, by applying a fixed heat flux of 500 kW/m². (ii) After the deposition process, pool boiling experiments were carried out on each of the copper surfaces coated with maghemite nanoparticles using deionized water as working fluid at atmospheric pressure and under saturated conditions. All samples were submitted to metallographic, roughness and wettability analysis. Changes in the boiling surface morphology, wettability and thermal resistance of the heating surface owing to nanoparticles deposition are dependent on the heating mode. Besides, as the nanofluid concentration increases the surface roughness also increases, and the higher the nanofluid concentration, the lower the contact angle of water on the coated surface. The heat transfer performance depends on the nanofluid concentration, the original surface roughness and the heating mode.

Flow pattern were studied experimentally during flow boiling of R-290 (propane) and R-600a (isobutane) inside a horizontal small tube (inner diameter ID = 1.0 mm). The effects of heat flux, mass velocity and vapor quality have been investigated. The tests were conducted at heat fluxes from 5 to 60 kW/m², mass velocity from 240 to 480 kg/m²/s at 25 °C saturation temperature. The main patterns observed for both refrigerants were plug, slug, churn, wavy-annular and smooth-annular. Bubbly pattern was observed only for specific conditions of R-290.

A numerical simulation of a vertical, upward, isothermal two-phase flow of air bubbles and water in an annular channel applying Computational Fluid Dynamics code (CFD) was carried out. The simulation considers an Eulerian frame, with two-fluid model, specific correlations for turbulence model considering the dispersion and bubble induction turbulence. The work intends to assess whether the code represents the physical phenomenon accurately by comparing the simulation results with experimental data obtained from literature. The annular channel adopted has equivalent hydraulic diameter of 19.1 mm, where the outer pipe has an internal diameter of 38.1 mm and inner rod 19.1 mm. To represent this geometry, a three-dimensional mesh was generated with 960000 elements, after a mesh independence study. The void fraction distribution, taken radially to the flow section is the main parameter analyzed besides interfacial area concentration, interfacial gas velocity, diameter and distribution of bubbles.

The present work addresses the effect of interfacial shear on the simulation of viscous oil-gas flows with the 1D Two-Fluid Model. An optimization procedure is employed in order to develop new expressions for the interfacial friction factor based on experimental measurements of stratified flow cases. In such methodology, a steady-state fully developed version of the 1D Two-Fluid Model is used and good results are obtained in the optimization procedure of the new expressions by the model. They are then used for simulating slug and stratified flow cases through the numerical solution of the 1D Two-Fluid Model in fine meshes (Slug Capturing methodology). Results are explored via mesh convergence tests and analyzes of the influence of a direct increase of the interfacial shear on the results. The study reveals that expressions for the interfacial friction factor elaborated based on methodologies which use the steady-state fully developed 1D Two-Fluid Model are not necessarily directly applicable to the Slug Capturing framework, which intrinsically predicts the interfacial dynamics. Additional care must be taken due to ill-posedness of the model. Finally, it is concluded that future expressions for the interfacial friction factor should include probably include dynamic effects.

The presence of gas in the centrifugal pump causes an undesired effect of reducing the pump performance. The increase in gas flow rate causes a reduction of head and flow rate developed by the centrifugal pump. Several studies were developed to understand the effect of gas on the centrifugal pump performance. However, just a few of them are interested in understanding the dynamics of bubble motion inside the pump. This paper presents a numerical study on the influence of operational conditions on the bubble trajectory. One stage of a centrifugal pump is used which consists of an intake pipe, an impeller, a diffuser and a simple extension of the diffuser. The Eulerian-Lagrangian “one way” approach is used to analyze the bubble motion inside the centrifugal pump. Numerical results are validated with experimental data from literature, which shows a good agreement. Results show that the operational conditions have an important influence on the bubble trajectory. Higher flow rates drag the bubbles outside the impeller, while the increase in rotational speed deflects the bubbles toward the pressure side of blade.

The production development in the Pre Salt presents several challenges to overcome such as long distances from the coast, deep reservoirs with low temperatures, high-pressure levels, deep water and others. This article aims to study the gas density influence in the pressure drop through a pipeline. To study this, it was developed a multiphase model at Olga simulator (two-phase fluid model), using a R 410 refrigerant mixture as fluid. The fluid properties were generated through PVT Sim software, being R410 refrigerant modeled from its pure components: R-32 and R-125. A flow rate range was evaluated varying downstream pressure for each temperature initial conditions. Besides, it was evaluated the following profiles: void fraction, quality, gas and liquid density, viscosities, superficial velocities, in situ velocities, gravitational and frictional pressure gradients. As it was expected, the higher gas density, the higher gravitational pressure gradient is. The increasing of frictional gradient pressure can be explained by increasing in situ gas velocities, although mixture density decreasing. An increasing of gas quantity implies in an increasing mixture viscosity, which in turns, contributes to the increasing of frictional gradient pressure, at the same time no changes in liquid an gas viscosities were observed. These simulation results presents consistent with that was expected.

The problem of deposition of solid particles on a porous substrate is common to a variety of industrial applications, such as fluidized beds, controlling of the emission of pollutants, drying by atomization and also in drilling operation of oil and gas well. In this work, the numerical simulation of the particle flow through a vertical porous channel is proposed. The porous substrate is represented by a heterogeneous model, where the solid domain is described by disconnected cylinders immersed in a water- glycerin solution. An Euler-Lagrange approach is given by the combination of the Dense Discrete Phase Model (DDPM) with the Discrete Element Method (DEM), respectively, to perform the coupled solution of the continuum (fluid) and the discrete phases (particles). Results show the variation of the porous domain permeability, diameter and mass flow rate of the particles over both the pressure and permeability of the outcome medium. For specific conditions, the increase of the particles diameter reduces the permeability of the resulting medium. The raise of the injected particles concentration is proportional to the pressure drop and to the growth in the particle bed thickness, reducing the permeability through the medium.

The present study proposes a transient simulator able to reproduce important phenomena inherent to petroleum production systems based on the non-isothermal Drift-Flux model. The system of equations considers a three phase flow regardless the liquid-liquid drift velocity, assuming mass transfer among the phases and heat transfer counter-currently between gas injection and the production systems. Gas injection valves connecting service line and output line valves, important to system operation, as two master valves and surface choke besides of pumping facilities are also assumed in the mathematical formulation. The fluids´ properties are estimated using a black oil model. The solver utilizes the finite volume method with a semi-implicit approach making use of the upwind first order scheme with staggered grid. Void fraction and liquid amount between the liquid phases are evaluated explicitly. The couple between velocities field and pressure is implicit by building a global matrix. It is not made an iterative process for the resolution of these fields. The temperature field is obtained in an uncoupled way after the volumetric fraction, mass flow rates and pressure calculus. Pressure, temperature and holdup trends are analyzed upstream and downstream of the master valve. The profiles of these interest variables as well as the superficial velocities along the production system are also reported showing that the thermal transient process is the slowest. This feature is due to the diffusive heat transfer in wall pipeline and in the well. The steep decay and the sudden increase of pressure at upstream and downstream regions, respectively, can result in operational problems depending on its magnitude.

Wire-mesh sensors are flow imaging devices which produce three-dimensional data of void fraction distribution at high resolution thus being an appropriate tool to investigate two-phase gas-liquid flows. Slug flow is typically found in petroleum production lines. This type of flow is characterized by the intermittent occurrence of gas bubbles and liquid slugs along the pipe. An important issue of these flows is the existence of a variety of regimes, depending on the flow rates of gas and liquid. The quantitative and qualitative information about shapes of the bubble nose and tail allows to study and to model the flow characteristics in order to increase safety and profit margins in operation of pipelines. In this paper we describe a methodology to determine typical bubble shape of gas-liquid slug flow, which are based on ensemble mean and median approaches, for a set of identified bubbles in a given experiment. Results show that both approaches produce similar estimations, however since median is a type of robust estimator, contours of bubbles are better defined. Three-dimensional images of typical bubbles, for five different operational conditions, are generated and reveal some details about bubble shape.

In order to design and operate oil production systems optimally, it is essential to rigorously anticipate the behavior of two-phase flow in pipelines. The present work aims to validate the results of the total pressure gradients (sum of the gravitational, friction and acceleration pressure gradient) and liquid holdup obtained through the homogeneous no-slip model, the empirical method proposed by Beggs & Brill, the mechanistic model proposed by Shoham (2006) for bubble flow, the mechanistic model developed by Ansari et al. (1994) for slug flow and the mechanistic model developed by Alves et al. (1991) for annular flow. For this, input data were considered, and then the described models were plotted in electronic spreadsheets by using macros and programming in Visual Basic for Applications (VBA). These models were then validated through the values obtained of liquid holdup and total pressure gradient from the OlgaS correlation of the software PIPESIM®. With the elaboration of this work, it became clear the importance of estimating the pressure gradient in a system. Any improvement or calibration that can be obtained by analyzing the best modeling can result in extraordinary profits in oil production systems. The individualized description of the components of the total pressure gradient enables to develop or operate more efficiently in the wells, such as injection of friction reducers.

In this paper, an analysis of particulate matter dispersion in indoor spaces was made using a CFD (Computational Fluid Dynamics) model in steady state, on a commercial software, FLUENT. An Eulerian method was used to solve the fluid flow, applying the renormalization group (RNG) k-ε turbulence model and a DRW (Discrete Random Walk) Lagrangian approach was used to predict the particle trajectories accounting for the turbulent dispersion. The numerical results obtained were compared with experimental data reported in the literature. The simulated velocity fluid flow agrees well with the reported experimental measurement. The Lagrangian model presents some discrepancies in the particle phase concentration on the bottom side, the predicted concentration is lower than expected, over-predicting the particle transport and the deposition rate, probably due to large turbulent kinetic energy estimation and the near wall region treatment.

Choke valves are widely used at the wellhead as a safety device in order to maintain a high pressure upstream the valve, avoiding the killing of the well, and can be operated as a closing device to isolate one well from the production pipeline. Pioneer authors used empirical correlations to predict the flow, based in fitting curves obtained from experimental data: representative examples are the correlations proposed by Gilbert (1954), Ros (1961) and Ashford (1974). Later, more accurate approaches were developed based on mass, momentum and energy conservation equations, seeking to solve them with some simplifications: the models from Sachdeva et al. (1986), Perkins (1993), Al-Safran and Kelkar (2009) and Schüller et al. (2003, 2006) can be cited as references. This paper reviews some of the models for predicting the flow rate of a gas and liquid mixture through a choke valve, widely applied at gas wells and petroleum industry. The basic assumptions are reviewed, such as the thermodynamical gas evolution, slippage between the phases and consideration of the upstream kinetic energy and diameter ratio. Two models are chosen to be reviewed: the homogeneous flow model proposed by Sachdeva et al. (1986) and the model proposed by Al-Safran and Kelkar (2009). The input parameters to compare the solutions when applying each model are based on the experimental data published by Schüller et al. (2003, 2006). Considerations for developing a general expression to predict the flow through the valve and discussions regarding the discharge coefficient are presented.

In this work, a linear stability analysis for pipeline-riser system is presented. The model considers continuity equations for liquid and gas phases and a momentum equation for the mixture where friction effects are taken into account. To evaluate the void fraction, it is adopted the drift flux model, based on Bendiksen (1984) correlation, for slug flow in the riser and the Taitel and Dukler (1976) approach for the stratified flow in the pipeline. The model also considers a gas-oil-water flow, so it is adopted a black-oil phase equilibrium model for the fluid characterization McCain (1990). To perform the stability analysis, the equations are linearized around the stationary state and discretized by the finite difference method. From the linearized system, it is evaluated the stability of the stationary state by the roots of the characteristic polynomial from the eigenvalue/eigenvector problem. Stability maps are presented as numerical results for a real oil production system. The preliminary results obtained are compared to Nemoto and Baliño (2012) and they show an excellent agreement.

Wire-mesh sensors have been widely applied to investigate gas-liquid flows in past where measured resistance or capacitance distributions over sensor crossing points are converted into gas or liquid holdup distributions. In this work we report on the application of the wire-mesh sensor for the measurement of cross-sectional solid concentrations in solid-gas-liquid flow. As the electric permittivity of solid particles are different from those of gas, water or oil, measuring this property can be used as an indication of solids distribution. The results indicate that the wire-mesh technique can be applied as a tool for the fluid dynamic study of three-phase liquid–gas–solid systems.

Two-phase flows are very common in different industrial applications. The knowledge of the parameters and characteristics of the flow can guarantee a safe and efficient operation of plants. In the past, many techniques have been developed to measure multiphase flows. In this study, we apply a direct-imaging sensor to characterize gas-liquid slug flow. Direct images generated by the non-intrusive sensor are compared with the images from a reference sensor called wire-mesh sensor. While the reference sensor produces cross-section images of void distribution, the direct-imaging sensor produces images which still need some further interpretation to describe some flow features. This paper sheds some light on how direct-images can be used for slug flow characterization.

Pulsating heat pipes are a special type of heat pipes that do not need a separate capillary structure for liquid feeding the evaporator. It could be related to a thermosiphon but according to some studies it can work even in the absent of gravity forces. The objective of this paper is to present a study on the influence of gravity in the performance of pulsating heat pipes, as a limiting characteristic for applications of these devices. A updated literature review of the experimental studies is presented showing the conclusions about the influence of gravity in the performance of pulsating heat pipes

a Engineering School of São Carlos, University of São Paulo, USP, São Carlos – SP

b Institute of Science and Technology, Federal University of the Jequitinhonha and Mucurí Valleys, UFVJM, Diamantina – MG

This paper presents a numerical model developed on GT-SUITE® to describe the thermal-fluid behavior of a single-compartment household refrigerator during start-up and cyclic operations. A domestic refrigerator from a study available in the literature was considered and the geometrical and performance parameters of the components were applied as input data. Empirical correlations for refrigerant side and air-side heat transfer correlations, as well as friction factors were considered. The model is capable of simulating the start-up operation based on refrigerant charge and ambient temperature. The simulation model was used to reproduce pull-down tests for different ambient temperatures, namely 21 °C, 32°C and 43°C, and for cyclic operations simulated by acting over the thermostatic valve model. For pull-down test simulations, transient variations of several variables were analyzed. During cyclic operation, the model can predict on-off behavior of heat exchangers and compressor, including such parameters difficult to measure experimentally, as refrigerant migration in the system. Although no experimental data were available for comparison, the model provided good qualitative predictions of the refrigeration system as well as the behavior of the air inside the refrigerator compartment during both pull-down and cyclic operations

An experimental investigation was carried out to elucidate the effect of the channel inclination on two-phase flow characteristics. Air/water flow was investigated inside a rectangular channel, 6.0 mm deep and 6.5 mm wide. The channel inclination varied from -90º to +90° relative to the horizontal plane. Flow patterns were identified and pressure drop was measured for mass velocities between 90 and 760 kg/m²s, corresponding to gas and liquid superficial velocities ranging from 0.09 to 19.4 m/s, and from 0.1 to 0.76 m/s, respectively. Flow patterns maps were developed according to the following approaches: (i) subjective approach based on flow images captured through a high-speed video camera; (ii) objective approach based a data-grouping algorithm, using metrics based on signals from the two-phase flow. Three flow patterns were identified: bubble, intermittent and annular. Stratified flows were not observed. Major differences in flow patterns transitions are observed comparing upward and downward flow. In general, the total pressure drop increased with increasing channel inclination, due to the contribution of the gravitational pressure drop parcel. In this study, the frictional pressure drop was estimated from the total pressure drop using different void fraction methods to estimate the gravitational parcel during inclined flow.

Phase-change heat transfer is significantly influenced by surfaces’ wettability, which has turned this into one of the hottest investigated topics in multiphase field. The objective of the present work is to evaluate the dynamic wettability of neat and alumina-coated aluminum plates. The alumina-coated plate was produced through pool boiling of 300 ml of a water-based nanofluid containing 0.1% in volume of 20–30 nm γ-Al2O3 nanoparticles over an as-received aluminum plate. The wettability of both neat and alumina-coated plates was assessed by side-on and top-down methods, using a high-speed camera to acquire images of 8 µl deionized water droplets spreading on these surfaces. The contact line displacement and velocity were evaluated using both methods and the time-variation of contact angle was assessed by the side-on method. Good agreement and repeatability among the tests were observed. The deposition of nanoparticles on the aluminum plate resulted in a superwetting surface, and it could be noted that the spreading mechanism changed from inertially-driven to capillarity-driven on such surface.

The shortage of new light oil deposits has led to the exploration of heavy oil reserves, which exceed 400 billion barrels not yet produced in the world. However, the transportation and refining of heavy oil are very expensive. Due to this, chemical and petrochemical industries are looking for technologies to reduce operating costs. The concept of flowing oil through a core annular flow pattern is one of the most promising techniques to reduce power consumption during the transport of viscous fluids in pipelines. In this work, a hydrocyclone device was employed to promote a core annular pattern in a vertical section of an experimental bench using different compositions of an oil-water mixture. To evaluate the efficiency of the hydrocyclone, a flow fractionator device was installed at the end of the pipeline loop and had the objective of separating the entire flow into two sections: annular and core. The obtained data showed that the hydrocyclone attended the proposal of organizing the biphasic flow towards a core annular pattern, reducing in about 70 % the amount of oil in the annular section for low oil concentration mixtures as low as 20 %.

The evolution of interfacial waves on a stratified flow was investigated experimentally for air water flow in a horizontal pipe. Waves were introduced in the liquid level of stratified flow near the pipe entrance using an oscillating plate. Mean height of liquid layer and fluctuations superimposed to this mean level were captured using high speed cameras. Digital image processing techniques were used to detect instantaneous interfaces along the pipe. The driving signal of the oscillating plate was controlled by a D/A board that was synchronized with the acquisitions. This enabled to perform phase locked acquisitions and to use ensemble average procedures. Thereby, it was possible to measure the temporal and the spatial evolution of the disturbances introduced in the flow. In addition, phase locked measurements of the velocity field in the liquid layer were performed using standard planar PIV. The velocity fields were extracted at a fixed stream wise location, whereas the measurements of the liquid level were performed at several locations along the pipe. The assessment of the set-up was important for validation of the methodology proposed in this work since it aimed at providing results for further comparisons with theoretical models and numerical simulations. Results show that linear waves were observed for liquid level oscillations lower than about 1:5%. Eigenfunctions in the liquid layer related to interfacial modes were measured experimentally for the first time. For moderate holdup levels, the eigenfunctions clearly show that interfacial modes are decoupled from inner modes which are related to wall turbulence.

The present work studies the effects of the orientation of gas injection nozzles on the global and local properties of vertical liquid crossflows. Experiments are carried out to investigate the effects of gas injection in counter-current (negative angle), orthogonal and co-current (positive angle) flow geometries. Different liquid (4) and gas (4) flow rates are combined to generate flow patterns with distinct physical effects. The flow properties are characterized through Particle Image Velocimetry and Shadow Sizing. Special hold up valves are used to estimate the gravitational component of pressure drop. This term is compared with the pressure gradient due to three additional affects: wall frictional, energy dissipation due to bubble agitation and acceleration.

Experiments on slug flow were carried out with compressed air and solutions of carboxymethylcellulose (CMC) in a 44.2 mm diameter horizontal pipe. Bubble velocities and frequencies of passage were obtained through a high-speed digital camera; pressure drop was measured with a differential pressure transducer. The flow behavior was found to be heavily influenced by the rheological properties of the continuous phase. In particular, aeration, slug frequency and pressure drop were largely increased. Pressure drop predictions obtained through two modified mechanistic models were compared to the data. The impact of the proposed friction factor formulation on the calculated properties of the slug flow is evaluated. For the best set of equations, RMS errors of 15.8% were obtained.

This paper presents a study of the heat and mass transfer behavior in falling liquid films technology for refrigeration (T = 253[K]) / air-conditioning (T = 280[K]) applications. Ammonia-water (NH3 – H2O) and Lithium bromide-water (LiBr – H2O) absorption refrigeration cycles (ARC) have been simulated to find the typical operation condition, in which the mass and energy equations were implemented through the Engineering Equations Solver (EES). Heat and mass transfer correlations used in the absorption processes have been evaluated for both working fluid pairs, in which a mapping of the possible heat and mass transfer values is presented. The study allowed comparing the two technologies using the same operational conditions. The ascertainment that the transfer correlations may behave differently has been showed. Finally, the study suggests that future researches about heat and mass transfer behavior should be to carry out for realistic operational condition of the absorption refrigeration cycles.